How can I let a teamcity command line build step pass if the exit code is not zero?

I have a command line 'custom script' build step involving robocopy. Unfortunately when robocopy is successful, it returns exit code 1 instead of the more common exit code 0. When it does this, it fails my teamcity build configuration.

How can I tell teamcity to fail the build if the exit code != 1 for this build step only? Can this be done? What about editing project-config.xml somehow?